The Ultimate God is located at the bottom of the Aerial Fortress Seibal, and is sleeping since ancient times. In the past, rituals were conducted between Duel Priests, in order to combat and seal this being, who people feared. It is said that should a Duel Priestess lose the ritual Duel, the Ultimate God shall awaken. It also appears that in order to keep this God sealed, not only the Duel Priestess must win, but she should also be offered as a sacrifice for the God.
In the thirtieth century B.C., Rex and Roman became Duel Priests and conduced the Ritual of the Sun and Moon attempting to revive this God who was said to be able to realize any wish - they wanted to revive Ix Quic Goodwin, the previous Duel Priestess who was sacrificed for the ritual. For that purpose, they convinced the Duel Priestess from that time to lose on purpose, which caused the sun to hide and a disaster to happen, killing many people. Rex and Roman then headed towards the Aerial Fortress Seibal in order to reach the God; however, Rex was completely dominated by its colossal dark miasma, causing him to go crazy.In the present, Rex and Roman use Sect Ijuin and Akiza Izinski as the Duel Priests to conduce the Ritual Duel once more in an attempt to revive the Ultimate God. For that purpose, Goodwin always planned on Akiza's defeat.
After Akiza loses the ritual Duel, the Ultimate God opens its eyes. With Sect's victory, he becomes the Supreme King of the Earthbound Lock. Rex, Roman, Yusei and Jack then conduce Duels inside Seibal in order to decide the Supreme King of the Heavenly Lock, who would conduce a Duel against the king of the Earthbound Lock which may open the Ultimate God's door and set him free.
Finally, Yusei becomes the Supreme King of the Heavenly Lock, and Duels against Sect. Meanwhile, the defeated Duel Priestess, Akiza, is offered as a sacrifice, with the Ultimate God slowly draining her life. In the beginning of the final ritual Duel, the Ultimate God starts its ressurection, and produces a roar which thrills Yusei and Jack due to its power.
- ↑ Yu-Gi-Oh! 5D's Ride 34: "Resolution!!"
- ↑ 2.0 2.1 2.2 Yu-Gi-Oh! 5D's Ride 40: "Ritual of the Sun and Moon!!"
- ↑ 3.0 3.1 Yu-Gi-Oh! 5D's Ride 51: "Recollection...!!"
- ↑ Yu-Gi-Oh! 5D's Ride 42: "Insect King Sect!!"
- ↑ Yu-Gi-Oh! 5D's Ride 45: "The Way Towards Supreme King of the Heavenly Lock!!"
- ↑ Yu-Gi-Oh! 5D's Ride 52: "The Ultimate God Roars!!"